1. Field of the Invention
The present invention relates generally to audio processing and, more particularly, to noise reduction of speech audio.
2. Description of the Background Art
Noise reduction in audio signals has approximately a fifty year history. Early analog methods for performing this task relied on amplification of the desired signal relative to the inevitable background noise. This was accomplished by selectively amplifying frequency bands that are most susceptible to noise, and later reducing the amplification for playback (see the work of Dolby). In order for this approach to work, special recording and playback equipment must be used.
Modern approaches to noise reduction primarily use a time-frequency (e.g. spectrogram) approach. In these approaches, an audio signal is first decomposed into frequency bands. Next, the frequency of the noise component of the signal is analyzed. This frequency component is then subtracted out of the signal. The signal is then reconstructed, with the frequency components of the noise removed. This approach is good at removing noise, but also damages portions of the desired voice signal. This is more pronounced at higher frequencies, giving the denoised audio a “muffled” quality.
Accordingly, what is desired is a denoising mechanism that does not noticeably affect voice signal quality.